U.S. Pat. No. 4,784,573 (Ress, Jr.) issued on Nov. 15, 1988, describes a turbine rotor with hollow, air cooled rotor blades that are integrally secured to the rotor hub, for example, by diffusion bonding. The blades are thickened at their blade foot that is connected to the rotor hub, preferably to a slightly raised plateau forming an integral part of the hub. Diffusion bonding or welding as such is known from U.S. Pat. No. 4,526,312.
It is a disadvantage in the manufacture of rotor disks with integral blades that conventionally applied welding methods require a high pressure in order to provide the required frictional movement between the rotor blade and the welding stub or plateau on the rotor hub to accomplish friction welding for forming an integral unit in which the blade foot is butt-welded to the rotor hub. These conventionally required high pressures have made it difficult heretofore, if not impossible, to produce rotor disks with hollow blades integrally secured to the rotor hub because hollow rotor blades cannot withstand these high working pressures. Incidentally, rotors with hollow rotor blades integrally secured to the rotor hub are referred to in the relevant literature as BLISK.
It has been found that the above outlined problem becomes even more pronounced if it is intended to weld hollow blades made of two hollow blade sections or blade shell parts to the rotor hub. The blade sections are conventionally soldered to each other along their entire radial length, whereby the solder is provided between matching seam or joint surfaces of the two blade sections or shell parts. The blades are weakened, particularly in the blade foot area by the solder seam extending along the entire radial length of the respective hollow blade.
German Patent Publication 2,510,286 (Weiler et al.) published Sep. 16, 1976, discloses a method for producing a connection between a rotor hub or disk primarily made of steel with rotor blades primarily made of titanium. It is known in this connection to connect the blades to the hubs by soldering, electron beam welding, diffusion welding or friction welding. However, problems have been encountered in that the connection did not have the required strength presumably due to the formation of brittle phases, particularly in the area of the welding seam and presumably also due to the different heat expansions in response to the welding heat. Weiler et al. solve this problem by first blast welding a steel plate and a titanium plate to each other to form a two layer plate. Then the steel plate layer of the two layer plate is welded to the steel rotor hub or disk and the titanium plate layer is welded to the titanium blade of the rotor disk.
German Patent Publication 1,007,565 (Sedlmeir) published on May 2, 1957 discloses hollow turbine blades for gas turbines charged with a gaseous drive medium. The individual blades have a particular cross-sectional configuration which is so constructed that the hollow cross-section increases from the blade foot to the blade head or tip to such an extent that in this direction, namely the radial direction, the material cross-section of the blade tapers off to become smaller while achieving an increase in the total cross-section of the blade. As a result less strain is applied to the connection between the blade foot and the rotor hub, whereby the respective r.p.m. of the rotor may be increased. Particular problems with the connection between the blade and the rotor hub are not described, however such problems do exist as described above.
These problems become even more pronounced when the individual hollow rotor blades are assembled of two matched blade sections or blade shell parts. Conventional welding operations have not succeeded in securely attaching such hollow two-section blades to the rotor hub. The joining seam which is normally made of solder is ripped open particularly in the blade foot area particularly in the butt-welding area between the blade foot sole and the blade foot welding stub or plateau.